FR2600081A1 - PROCESS FOR SEPARATING RARE EARTHS - Google Patents

Abstract

THE PRESENT INVENTION CONCERNS A PROCESS FOR SEPARATING RARE EARTHS CONTAINED IN ORES OR CONCENTRATES RICH IN FLUOCARBONATES FROM RARE EARTHS, IN PARTICULAR BASTNAESITE. THE OBJECT OF THE INVENTION IS A PERFECTED PROCESS FOR SEPARATING THE NEODYM, POSSIBLY IN ASSOCIATION WITH THE PRASEODYM OF THE OTHER RARE EARTHS CONTAINED IN THE BASTNAESITE, THIS PROCEDURE BEING CHARACTERIZED BY THE FACT THAT IT CONSISTS of: PERFORMING THE BASTNAESITE BASTNAESITE; TO CARRY OUT A CAREFUL LEACHING OF THE CALCINATED BASTNAESITE USING A NITRIC ACID SOLUTION; -A PROCEED WITH THE SEPARATION AND PURIFICATION OF THE NEODYME POSSIBLY IN ASSOCIATION WITH THE PRASEODYME BY LIQUID-LIQUID EXTRACTION.

Description

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  PROCESS FOR SEPARATING RARE EARTHS

  The present invention relates to a process for separating rare earths contained in ores or concentrates rich in rare earth fluocarbonates, in particular bastnaesite. More specifically, the subject of the invention is an improved process for separating neodymium, optionally in combination with the

  praseodymium of other rare earths contained in bastnaesite.

  The term "rare earths" used according to the invention

  includes rare earth elements having atomic numbers from 57 to 71 inclusive and yttrium of atomic number equal to 39.

  In the following description of the present invention, the term "ceric rare earth" means the lightest rare earth elements starting with lanthanum and extending to neodymium according to the atomic number and by "yttric rare earths". heavier elements of the rare earths according to the atomic number, starting with the samarium and ending with lutetium and including yttrium. In addition, "trivalent rare earths" refer to rare earth elements having

  Atomic values equal to 39, 57, 59 to 71.

  The term "didyme" is the common name of a mixture

  of neodymium and praseodymium regardless of their proportions.

  The term "bastnaesite" used broadly refers to a

  rare earth ore comprising rare earth fluorocarbonates with or without other constituent including a mineral gangue and the concentrates of these ores.

  The development of rare earth magnets and more particularly those based on neodymium and praseodymium alloy with iron requires the implementation of

  separation performance technically and economically.

  The processes currently practiced for purifying rare earths from ores are directed either towards a valorization of the whole of the rare earths separated, which is cumbersome and expensive, or towards a valorization of a fraction rich in rare earths of price high especially europium, the land

rare yttric and yttrium.

  Many processes have been described and are practiced industrially with the above objectives, starting from the conventional rare earth raw materials, monazite,

bastnaesite or xenotime.

  The methods proposed in the case of a complete recovery of the rare earths generally implement a soda attack followed by a redissolution by hydrochloric or nitric acid hydroxides obtained. On the solutions of chlorides or nitrates of rare earths, the rare earths are separated from each other by successive liquid-liquid extraction operations. In the case of bastnaesite, it is possible to perform, as described in Deco Trefoil, November-December 1967 p.9, a precalcination of the ore which makes it possible, during the recovery with hydrochloric acid, to solubilize only a part of the cerium with the mixture of other rare earths. From the rare earth chloride solution, solvent separation of the europium is carried out

  and the fraction of yttric rare earths.

  As already mentioned above, these processes if they

  allow recovery of neodymium and praseodymium are poorly suited to do so under satisfactory economic conditions 25 with respect to the intended application.

  The object of the present invention is to provide a particularly efficient and economical method of separating the

  neodymium or didyme contained in bastnaesite.

  The subject of the present invention is precisely a process for separating neodymium or didymium from the rare earths contained in bastnaesite, characterized in that it consists in: - calcining the bastnaesite, - performing a gentle lixiviation of the bastnaesite calcined with a nitric acid solution which makes it possible to solubilize neodymium and trivalent rare earths with the exclusion of cerium and traces of thorium which are in the form of an insoluble residue which is then separated, to proceed to the separation and purification of neodymium or didyme by liquid-liquid extraction between the aqueous phase constituted by the aqueous solution of rare earth nitrates recovered in the preceding stage and an organic phase containing an agent of extraction insoluble in water and then to recover the

  neodymium or didymium of the organic phase.

  Under the conditions of the present invention, it is found that excellent cerium / other rare earth selectivity is obtained during the selective leaching carried out using the nitric acid solution. Moreover, it is demonstrated that the thorium has a behavior similar to that of cerium during leaching, so that the process of the invention has the advantage of simultaneously leading to the elimination of cerium and

  traces of thorium contained in bastnaesite.

  However, small amounts of cerium and thorium can be solubilized in the nitric acid solution. In the process according to the invention, the solubilized cerium is essentially in the tetravalent state, which makes it easy to separate it and, together with the thorium from the mixture, trivalent rare earth nitrates, for example, by a pre-neutralization operation with during which the small amounts of cerium and thorium are removed in the form of a solid residue which also contains the

  fluorine solubilized in small amounts during nitric recovery.

  Gentle leaching of bastnaesite with nitric acid solution selectively solubilizes trivalent rare earths except cerium whose soluble traces are predominantly in tetravalent form. Such a selective leaching is known and described with hydrochloric acid for example in FR 1 503 042 but in such a case, the cerium is solubilized in the trivalent state and is therefore not easily

  separable from other trivalent rare earths.

  Moreover, the fact of operating in a nitric medium, widens the possibilities of choice of the extraction solvent which is then used for the separation of the rare earths between them. In this case it is possible to use the anionic, cationic and solvating extraction agents, which is not the case in a hydrochloric medium which does not commonly allow the separation of

  rare earths only by cationic extractants.

  According to the invention, the source of rare earths is

  bastnaesite which is essentially a rare earth fluocarbonate.

  The rare earths present are essentially ceric rare earths, lanthanum, cerium, praseodymium and neodymium, and the other rare earths known as yttrics may represent up to about 8%, most often less than 2%, expressed by weight of oxides. totals. It is possible that there is also thorium present in an amount representing not more than 1.5% of the weight of the total oxides and most often in the state of

  traces, corresponding to less than 0.5% by weight.

  It is preferred according to the invention to use a bastnaesite ore containing more than 10% by weight of earth.

  rare expressed in rare earth oxides.

  However, it is more advantageous to operate on concentrates of bastnaesite ores obtained in a conventional manner by enrichment using physical techniques, grinding and flotation or gravity concentration on shaking tables and / or enrichment according to a chemical method, for example a treatment with an acid, in particular a dilute solution of hydrochloric or nitric acid having a concentration of about

  % in order to eliminate calcite.

  Concentrates of bastnaesite usually contain

  a rare earth content expressed in oxides ranging from 40 to 75%.

  The first step of the process of the invention is to calcinate bastnaesite at a sufficiently high temperature to transform the trivalent rare earths in a form that can be solubilized in the subsequent nitric acid leaching operation and transform the

  cerium in a form more difficult to dissolve.

  The calcination is carried out at high temperature so that said temperature is chosen to be greater than 400 ° C. Above, the temperature is not critical, but nevertheless good operating conditions combining efficiency and duration of the operation consist in working between 600 and 800 C. The duration of the calcination depends on the calcination temperature: it is shorter as the temperature is higher. The calcination operation usually lasts between

minutes and 3 hours.

  After the calcination operation, the calcined bastnaesite is carefully leached with an aqueous solution of nitric acid which makes it possible to solubilize selectively

trivalent rare earths.

  The concentration of the nitric acid solution is not critical: it can vary within wide limits, for example from 1 to 14 N, but it is preferable to use an aqueous solution of nitric acid of concentration 3 at 9 N. The amount of acid used is an important part of the process; it is adjusted according to the solubilization efficiency and selectivity sought for the separation of cerium from other rare earths. An excellent separation cerium / rare earth combined with a very good recovery of trivalent rare earths including neodymium is obtained by implementing an amount of acid corresponding to the stoichiometry of trivalent rare earths. This quantity may of course vary according to the origin of bastnaesite, which may lead to a variation in the distribution of the rare earths between them; however, most often bastnaesites contain about as much cerium as other rare earths and so in this case the amount of acid used corresponds to half of the stoichiometry of

  all rare earths including cerium from the original ore.

  The amount of acid preferably used is the amount corresponding substantially to the stoichiometry of trivalent rare earths, but it is possible to use an excess of up to 50% of the stoichiometric amount.

  The leaching is carried out at a temperature which is not

  not decisive and which can be chosen between 20 and 900C.

  The residence time in the leach solution depends

  to some extent ore and calcination conditions. It is usually between 30 minutes and 2 hours.

  Good separation conditions are obtained during a treatment at 60 C for a residence time of one hour. At the end of the operation, the aqueous solution of rare earth nitrates is separated from a solid residue according to a conventional liquid-solid separation technique, for example by filtration

or centrifugation.

  A solid residue containing is collected. essentially cerium mainly in oxide form and any traces of thorium. This residue can be valued as

what as concentrated cerium.

  With regard to the leaching solution recovered, it is indicated as an indication that when the process is carried out according to the conditions given preferentially, less than 10% of cerium and over 90% of the solubilized solution are solubilized in the leaching solution. Trivalent lands including neodymium initially

present in bastnaesite.

  - The concentration of rare earths in the solution obtained depends on the concentration of nitric acid used for leaching. Under the preferred conditions, the concentration expressed as rare earth oxides is between

and 500 g / l.

  - For the continuation of the separations it may be advantageous to eliminate the traces of tetravalent cerium and thorium present

  in the aqueous solution of rare earth nitrates.

  For this purpose a pre-neutralization is carried out using

  a base which is preferably ammonia or sodium hydroxide.

  The amount of added base which can be supplied in solid form, gaseous in the case of ammonia, or aqueous solution is determined so that the pH of the solution

  aqueous solution of rare earth nitrates is between 2 and 4.

  Under such pH conditions, tetravalent cerium, thorium and solubilized fluoride are precipitated upon nitric uptake. The precipitate is separated in a conventional manner and an aqueous solution of rare earth nitrates is collected from

  from which neodymium or didyme is separated.

  The separation of neodymium or didymium from other trivalent rare earths is carried out by liquid-liquid extraction between an aqueous phase containing the rare earth nitrates and an organic phase containing an insoluble extraction agent in water and then counter-extraction of neodymium or didymium of the organic phase. The extraction agent used in the process of

  the invention may be chosen from any extraction agent.

  having selectivity between rare earths.

  The extraction agent used can be chosen from

  the class of anionic extractants, solvent solvents, or cationic extractants.

  The anionic extraction agents used are in particular the long-chain organic compounds comprising

amine functions.

  The hydrocarbon chains of these compounds generally having

  preferably between about 5 and 30 carbon atoms.

  Among these, for example, mention may be made of: tertiary amines and in particular the products sold under the trade names Alamine 336 and Adogen 364 which consist of tertiary amines of formula R3N in which the hydrocarbon radical R has from 8 to 10 atoms of carbon, - quaternary ammonium nitrates and in particular products derived from products sold under the trade names Adogen 464 and Aliquat 336 which consist of quaternary ammonium salts of formula: [R3N-CH3] Cidans in which the radical hydrocarbon R has from 8 to 10 carbon atoms. The cationic extraction agents used are in particular organophosphorus acids; aliphatic or aromatic acids, halogenated or not; naphthenic acids; 0-diketones. Among these, there will be mentioned: - organophosphorus acids of general formula:

OR GOLD R

  R2O-O = O or R2-P = O or R2 - P = O

OH OH OH

  in which R and R2 represent aliphatic or aromatic hydrocarbon radicals such that the total number of carbon atoms of these groups is at least equal to 10. It is preferred to use di (2-ethylhexyl) phosphoric acid and bis (2-ethylhexyl) phosphonic acid; the carboxylic acids marketed by SHELL Chemicals under the name "VERSATIC" and which correspond to the general formula:

R1 / CH

C

R2 COOH

  in which R 1 and R 2 are substituted or unsubstituted hydrocarbon radicals, and in particular the "Versatic 10" acid (registered trademark) derived from the Shell carboxylation process for C 9 olefins and for which R 1 and R 2 are hydrocarbon radicals whose sum of the carbon atoms of the two radicals is equal to 7; The solvating extraction agents used are

  especially sulphoxides, neutral organophosphorus compounds.

  Among these, mention may be made of: sulfoxides of general formula: ## STR1 ## in which R 1 and R 2 are aromatic and / or aliphatic hydrocarbon radicals preferably having at least 4 carbon atoms and, for example, di-n-heptylsulfoxide, di-n-octylsulfoxide; the neutral organophosphorus compounds of general formula:

GOLD GOLD

R20 P = O or R20 P = 0 or

OR3 R3

R R20 P = 0 or R2-P = O

2 2

R3 R3

  wherein R 1, R 2 and R 3 are aromatic or cycloaliphatic and / or aliphatic hydrocarbyl radicals

  preferably having at least 4 carbon atoms.

  There may be mentioned, for example, tributyl phosphate, dibutyl butyl phosphonate, bis (2-ethylhexyl) ethyl-2 hexyl

  phosphonate, tri-n-octylphosphine oxide.

  Among these compounds, it is preferred to use tributyl phosphate. The organic phase according to the process of the invention optionally contains, in addition to the extraction agent, an organic diluent. As diluents that can be used, those usually used to carry out liquid-liquid extraction operations can be used. Among these, mention may be made of aliphatic hydrocarbons such as, for example, dodecane and petroleum fractions of the kerosene type: aromatic hydrocarbons, for example petroleum fractions consisting of a mixture of alkylbenzenes, especially the Solvesso type cups.

  marketed by EXXON.

  It is also possible to use a mixture of these diluents.

  The proportion of extraction agent in the organic phase is not critical and may vary within wide limits. However, it is generally advantageous that it be as high as possible. Thus, in the case of anionic and cationic extraction agents, a proportion of between 10 and 40% by volume relative to the organic phase leads to advantageous hydrodynamic separation conditions. In the case of solvating extractants, some of them (the less viscous)

  can be used pure, that is to say undiluted, which is extremely advantageous, because it leads to very significant extraction capabilities.

  The organic phase according to the process of the invention may also contain various modifying agents whose essential purpose is to improve the hydrodynamic properties of the system without altering the complexing properties of the extraction agent. Among the compounds that are suitable, there may be mentioned in particular alcohol-functional compounds and, in particular, heavy alcohols having a number of carbon atoms of between 4 and 15. A proportion of up to 20% by volume can be reported.

  to the organic phase is generally favorable.

  The separation of the trivalent lands is done between them

  by operating against the current on several theoretical stages of extraction, each stage being constituted by the mixing operation of decantation.

  The aqueous solution of rare earth nitrates to be separated is introduced at an intermediate stage of the countercurrent system thus achieving two separation zones "extraction" and "selective washing" on either side of this feed point. At each end of the device, partial reflux of the solutions containing the separated elements is carried out by carrying out the processes adapted to the properties of the extraction agent used, acid or base for a cationic extraction agent, water or steam. to dilute or concentrate in the case of solvating or anionic extraction agents. The effectiveness of separation depends on the number

  stages and the separation factor.

  For the separation calculation, reference will be made to the literature, especially to the articles of MM. J. HELGORSKY and A. LEVEQUE in the Encyclopedia ULLMANNS, Band 21. p. 235 to 271 (1982) and BROWN

  et al., J. Chem. Tech. Biotechnol. 29, 193-209 (1979).

  After the extraction and washing operations followed

  separation of the aqueous phase and the organic phase is carried out a counterextraction step of rare earths contained in the extraction solvent.

2600C 81

  The extracted rare earth (s) is separated in the organic phase by bringing it into contact with water or a slightly acidic solution of less than about 1 N, preferably a nitric acid solution, in the case of the agents. Anionic or solvating extraction or a more concentrated aqueous acid solution, greater than about 3 N, preferably an aqueous solution of nitric acid, in the case of cationic extraction agents. The extracted rare earth (s) is collected in the aqueous phase while the extraction solvent can be recycled.

in the extraction step.

  According to the invention, neodymium or didymium can be separated according to several embodiments. The order

  separations does not matter.

  To separate the neodymium, it is possible to carry out

  order 1, the separation of lanthanum-praseodymium from the mixture rare yttric neodymeterres and then separate the neodymium yttric rare earths or in order 2, perform the separation of the ceric rare earth (La, Nd, Pr) yttric rare earths and then separate 20 lanthanum and praseodymium neodymium.

  More precisely according to the order of separation, the aqueous solution of rare earth nitrates is brought into contact with the extraction solvent in order to extract the organic phase of the neodymium nitrates and the yttric rare earths and leave it in the aqueous phase. the nitrates of lanthanum and praseodymium, to counterextract the neodymium nitrates and yttric rare earths of the organic phase to recover them in the aqueous phase, to put this solution in contact with an extraction solvent so as to extract the nitrates of land rare yttrics in the organic phase and leave the neodymium nitrate in the aqueous phase. According to the separation order 2, the aqueous solution of rare earth nitrates is brought into contact with the extraction solvent so as to extract the yttric rare earth nitrates in the organic phase and leave the nitrates of lanthanum in the aqueous phase, of neodymium and praseo dyne, to bring this solution into contact with an extraction solvent so as to extract the neodymium nitrate in the organic phase and leave the lanthanum nitrate and of the praseodymium in the aqueous phase, to counter-extract the nitrate of neodymium phase

  organic to recover it in aqueous phase.

  In order to obtain didyme, lanthanum separation from the yttric rare earth-yttrix mixture can be carried out in a sequence of 1, followed by separating the yttric rare earth didyme or ordering the separation of the ceric rare earth elements (La, Nd, Pr ) yttric rare earths and then separate the lanthanum from the didymium. The neodymium or didymium solutions obtained according to the process of the invention are the raw materials of choice for the production of carbonates, chlorides, fluorides or oxides which are used as intermediates.

  especially in the manufacture of metals for magnets.

  The following examples illustrate the invention without limiting it. In the examples, the percentages given

are expressed by weight.

EXAMPLE 1

  This example illustrates the selectivity of the solubilization of cerium / trivalent rare earths during the gentle leaching of a

  calcined bastnaesite concentrate carried out according to the invention.

  Starting from a bastnesite ore concentrate [1] having the following weight composition: - loss on ignition: 17.4% - CaO: 0.25%

205 1.9%

- BaO: 1.75%

- F: 5%

Fe2O3: 0.3% - SiO2: 0.1%

- A23: 0.05%

  - Total rare earth oxides: 74.5% with the following distribution: CeO2: 51.0% La203 32.0% Pr60il: 4.2% Nd203 11.8% Sm23 0.8% 2u3 2Eu 3 0 , 1% 2d3 2Gd 3 0.2%

Y203: 0.2%

  ThO2: 0.3% In a muffle furnace the calcination of 1 kg is carried out

  of bastnaesite concentrate for 3 hours at 700 C.

  831 g of a calcined bastnaesite concentrate [2] having the following composition are obtained: - loss on ignition: 0.6% - CaO: 0.3%

- P205: 2.3%

- BaO: 2.1%

- F: 5.9%

  - total rare earth oxides: 89.6% The leaching operation of g of this calcined bastnaesite concentrate [2] is then carried out by treating it with 120 cm3 of 6.5 N nitric acid. The treatment is carried out with stirring at 60 ° C. and

residence time is 1 hour.

  The solid residue is separated from the nitrate solution of

  rare earths by filtration on BUchner.

  The recovered solution contains rare earths whose concentration expressed in oxides is 370 g / l, 4.8 g / l of fluorine and 0.35 g / l of Fe203. Its REE distribution is as follows: CeO2: 6.0Z La203 60.3% Pr6011: 8.3% Nd203 22.6% Sm203: 1.6% other rare earths: 1.2% These results correspond to the solubilization rate of the rare earths contained in the starting bastnaesite concentrate. CeO2: 5.6% 2La23: 90.6%.

P6011 95.3%

P6Oil Nd203 92.1% Sm203 93.1%

  It is noted that the solubilization yield of trivalent rare earths is 95.3% and that of cerium 5.6%.

  In addition, it is found that the soluble cerium is made up to 71.1% of cerium IV., The fluorine is solubilized at a rate of

9.8%.

EXAMPLE 2

  A series of tests is carried out according to the procedure of Example 1 in order to demonstrate the influence of the amount of nitric acid used on the cerium / rare earth selectivity.

  For this purpose, 4 fractions of 100 g of calcined bastnaesite concentrate [2] from Example 1 are taken.

  It is attacked according to the conditions of Example 1 by varying amounts of 6.5 N nitric acid which are indicated in

the following table I.

  After separation of the residues and analyzes, the following solubilization rates are obtained:

TABLE I

  Amount HNO 6.5 N 120 cm3 180 cm 240 cm 360 cm concentration of the rare earth nitrate solution expressed 370 310 340 240 in total rare earth oxides (g / l) I. solubilization rate (in%) lanthanum 90, 6 92.0 98.4 96.6 cerium 5.6 31.5 85.9 95.9 praseodymium 95.3 96.0 98.7 96.6 neodymium 92.1 90.7 90.9 96, 7 trivalent rare earths 95.3 95 96.2 97 thorium <1 15 62.5 87.5 fluorine 9.8 80 CeIV / This total 0.71 0.82 0.94 0.98 i In view of the results obtained, the amount of adequate acid

  corresponds to the stoichiometry of trivalent rare earths.

EXAMPLE 3

  This example shows with respect to example 2, the influence

  the concentration of nitric acid.

  The procedure is as in Example 2 except that the leaching of calcined bastnaesite concentrate [2] is carried out using an aqueous solution of 3.5 N nitric acid.

  The results obtained are shown in Table II.

26008 1

TABLE II

15

3 3 3 3

  quantity HNO3 3.5 N 220 cm3 340 cm 450 cm 670 cm concentration of rare earth nitrate solution

-150 145 135 95

  expressed as total rare earth oxides (g / l) solubilization rate (in%) _____________________- - - --- --- -------------------__ ___. Amanthane 75.8 94.9 95.1 96 Cerium 0.1 16.7 41.1 45 Praseodymium 83.9 95.3 95.3 95.5 Neodymium 83.5 93 93.7 95.2 Samarium 82, 1 93.1 93.1 97 rare rare triter rare earths 75.5 93.3 95.4 96 valents 95 6 thorium <1 12 50 63 The comparison of examples 1 and 2 shows that the concentration of the aqueous acidenitric solution is not critical.

EXAMPLE 4

  This example illustrates the separation of neodymium.

  The bastnaesite concentrate defined in Example 1 is calcined and subjected to a leaching operation arranged according to

  conditions described in Example 1.

  At the end of the treatment, the residue is filtered off

  solid containing essentially cerium of the aqueous solution of rare earth nitrates having a concentration expressed as rare earth oxides equal to 370 g / l.

  The tetravalent cerium and the traces of thorium present in said solution are eliminated by addition of an aqueous solution

  of 10 N ammonia until a pH of 3.5 is obtained.

  A solid residue containing all the tetravalent cerium and thorium is filtered off. The analysis of this residue shows that it also contains 86% of fluorine and almost all iron

  solubilized and 5% trivalent rare earths.

  The recovered rare earth nitrate solution has a concentration of rare earth oxides equal to 337 g / l and contains 0.7 g / l of fluorine, less than 10 mg / l of Fe203 and less than mg / l of ThO2 . Its distribution in rare earths is as follows: - 63.0% of La203 - 1.8% of CeO2 - 8.7% of Pr6O - 23.6% of Nd203 - 1.7% of Sm203 - 1.3% of other rare earths The concentration of this solution is carried out by evaporation of the said solution until a concentration is obtained.

  expressed as rare earth oxides of 490 g / l.

  This concentrated solution is then subjected to the operations

  successive liquid-liquid extraction conducted according to the embodiment illustrated in FIG.

  The equipment used for the rare-earth separation comprises: a first multi-stage liquid-liquid extraction tank of the counter-current mixer-settler type consisting of an extraction section (a) and washing (a ') having 40 theoretical stages and a counter-extraction section (b) of the rare earths extracted in the organic phase comprising 10 theoretical stages - a second liquid-liquid extraction battery consisting of a section of extraction (c) and a washing section (c ') comprising 40 theoretical stages and a counter extraction section (d) of the rare earths extracted in the organic phase

comprising 10 theoretical stages.

  The extraction agent used is tributyl phosphate. It is dissolved in kerosene at 75% by volume and

  the resulting mixture will be called extraction solvent.

260008 1-

  Before detailing the various operations, it will be specified that the extraction and washing-out and counter-extraction units are selected as inlets and outlets, the circulation direction of the

organic phase.

  The aqueous solution of rare earth nitrates is introduced at the 20th stage of the extraction-washing section at a flow rate of 2.05 liters / hour.

  in 2 the organic phase constituted by the extraction solvent at a flow rate of 8.8 liters / hour.

  At 5, at the outlet of the counterextraction section and against the current of the organic phase, water is introduced

  acidified (HNO3 - 0.1 N) at a flow rate of 4.4 liters / hour.

  At the inlet of the counter-extraction section at 6, an aqueous solution of rare earth nitrates containing neodymium and yttric rare earths is collected and concentrated by evaporation to a concentration expressed as rare earth oxides. 490 g / l. 0.54 liter / hour, which is the production of neodymium concentrate, is taken and the remainder, 1.78 liters / hour, feeds the extraction-washing section in 3 to achieve reflux. Neodymium concentrate has the following composition, expressed in rare earth oxides: - 88.4% of Nd203 - 0.5% of Pr60O 6.3% of Sm203 - 4.9% of other rare earths Pick up at the entrance from the extraction-washing section at 4, an aqueous solution of rare earth nitrates which is concentrated by evaporation to a concentration expressed as rare earth oxides of 490 g / l. 1.5 liters / hour, which is the production of a lanthanum concentrate, is withdrawn and the remainder is recycled to the first stage of the battery. This lanthanum concentrate has the following composition expressed in rare earth oxides: 85.9% of La203 - 2.4% of CeO2 - 11.7% of Pr601

  less than 0.01% of Nd203 and other rare earths.

  The regenerated extraction solvent that can be recycled is recovered at 7 at the outlet of the counterextraction section.

  in 2 in the extraction-washing section with the same flow.

  The neodymium concentrate defined above is

  feeding the second liquid-liquid extraction battery. It is introduced at 8 to the 20th stage of the extraction-washing section.

  At the inlet of the extraction-washing section, the organic phase consisting of the same extraction solvent is introduced at 9

at a rate of 3.15 liters / hour.

  At 12, against the flow of the organic phase, acidified water is introduced at a flow rate of 1.6 liters / hour.

  A solution of rare earth nitrates is collected at 13, which is concentrated by evaporation until a concentration, expressed as rare earth oxides, of 490 g / l is obtained. 0.06 liter / hour, which is the production of a yttric rare earth concentrate, is taken and 0.78 liter / hour is recycled in order to carry out the reflux. This yttric rare earth concentrate has the following composition, expressed as rare earth oxides: - 56.2% Sm203 - 43.7% of the other rare earth elements 25 - 0, 12% of Nd203 We collect at the entrance of the section extraction-washing in 11 an aqueous solution of neodymium nitrate which is concentrated by evaporation to a concentration expressed as rare earth oxides of 490 g / l. 0.48 l / h, which is the production of neodymium, is taken and recycled, the remainder at 9 with the organic phase. The purity of the neodymium produced is as follows: - 99.4% of Nd203 - 0.6% of Pr601l

  - less than 0.1% of other rare earths.

26O08 1

  The regenerated extraction solvent that can be recycled is recovered at the outlet of the counterextraction section at 14.

  in 9 in the extraction-washing section.

EXAMPLE 5

  This example illustrates the separation of didyme. According to the procedures described in Examples I and 4, the following operations are carried out: calcination of the bastnaesite concentrate defined in example 1 - controlled leaching of the calcined bastnaesite concentrate - separation by filtration of a solid residue from the solution of rare earth nitrates - pre-neutralization of said solution - separation by filtration of a solid residue from the rare earth nitrate solution concentration by evaporation of this solution until a concentration expressed as rare earth oxides of

490 g / l.

  This concentrated solution is then subjected to

  successive liquid-liquid extraction operations conducted in 20 according to the embodiment illustrated in FIG.

  The apparatus used for the rare earth separation comprises: a first liquid-liquid extraction battery consisting of an extraction section (a) and a washing section (a ') comprising 25 theoretical stages and a counter section; extraction (b) of the rare earths extracted in the organic phase comprising theoretical stages; a second liquid-liquid extraction battery consisting of an extraction section (c) and a washing section (c ') comprising 48 stages; theoretical and counter-extraction section (d) rare earths extracted in the organic phase

comprising 10 theoretical stages.

  The extraction agent used is tributyl phosphate

  in solution in kerosene at a rate of 75% by volume.

  The sequence of steps is described below.

  The aqueous solution of rare earth nitrates is introduced at the 20th stage of the extraction-washing section at a flow rate of 2.05 liters / hour. At the inlet of the extraction-washing section, the organic phase constituted by extraction solvent at a

flow rate of 11.1 liters / hour.

  At 5, at the outlet of the counterextraction and countercurrent section of the organic phase, acidified water (HNO 3 - 0.1 N) is introduced at a flow rate of 5.6 liters / hour.

  An aqueous solution of rare earth nitrates containing didyme and yttric rare earths is collected at the inlet of the counterextraction section at 6, which is concentrated by evaporation to a concentration expressed as rare earth oxides of 490. g / l. 0.72 liter / hour, which constitutes the production of the didyme concentrate, and the remainder, 0.89 liter / hour, is fed to the extraction-washing section in order to carry out the reflux. Didyme concentrate has the following composition expressed as rare earth oxides: 20 - 24.6% praseodymium - 66.8% neodymium - less than 0.01% cerium - 8.5% of other rare earths at the inlet of the extraction-washing section at 4, an aqueous solution of rare earth nitrates which is concentrated by evaporation to a concentration expressed as rare earth oxides of 490 g / l. 1.32 liters / hour is taken which is the production of a lanthanum concentrate and the rest is recycled to 2 on the 1st floor of the battery. This lanthanum concentrate has the composition expressed as rare earth oxides as follows: 97.2% of La 2 O 3 - 2.7% of CeO 2

  less than 0.1% of Pr6Oll and other rare earths.

  The regenerated extraction solvent that can be recycled is recovered at 7 at the outlet of the counterextraction section.

  in 2 in the extraction-washing section with the same flow.

26008 1

  The didyme concentrate defined above constitutes the supply of the second liquid-liquid extraction battery. We

  introduced in 8 to 22nd floor of the extraction-washing section.

  At the inlet of the extraction-washing section, the organic phase consisting of the same extraction solvent is introduced at 9 at a rate of 3.1 liters / hour.

  We introduce in 12, against the current of the phase

* organic, acidified water at a rate of 1.55 liters / hour.

  A solution of rare earth nitrates was collected at 13 and concentrated by evaporation to a concentration of rare earth oxides of 490 g / l. 0.06 liter / hour, which is the production of a yttric rare earth concentrate, is withdrawn and 0.78 liter / hour is recycled in 10 to make the reflux. This yttric rare earth concentrate has the following composition expressed as rare earth oxides: - 56.2% Sm 2 O 3 - 43.6% of the other rare earths - 0.19% Nd 2 O 3 collected at the entrance to the section extraction-washing in 11 an aqueous solution of neodymium nitrate and praseodymium which is concentrated by evaporation to a concentration expressed as rare earth oxides of 490 g / l. We take 0.66 1 / h which is the production of didyme and we recycle, the

stays in 9 with the organic phase.

  The quality of the didyme produced is as follows: - 26.9% of Pr60O - 73.1% of Nd203 2 3

  - less than 0.01% of other rare earths.

  The regenerated extraction solvent which can be recycled is recovered at 14 at the exit of the counter-extraction section.

  in 9 in the extraction-washing section.

26C0081

R E V E N D I CA T I 0 N S

  1 - A process for separating neodymium or didymium from the rare earths contained in bastnaesite, characterized in that it consists in: - calcining bastnaesite, - performing a gentle leaching of burnt bastnaesite with the aid of a nitric acid solution for solubilizing neodymium and trivalent rare earths excluding cerium and traces of thorium which are in the form of an insoluble residue which is then separated, - to proceed to the separation and purifying neodymium or didyme by liquid-liquid extraction between the aqueous phase constituted by the aqueous solution of rare earth nitrates recovered in the preceding step and an organic phase containing a water-insoluble extraction agent. then to recover the

  neodymium or didymium of the organic phase.

  2 - Process according to claim 1 characterized in that the bastnaesite contains more than 10% by weight of rare earths

  expressed in rare earth oxides.

  3 - Process according to claim 1 characterized in that the bastnaesite is concentrated and contains from 40 to 75% by weight

  rare earths expressed as rare earth oxides.

  4 - Process according to one of claims 1 to 3 characterized

  in that the calcination temperature is greater than 25 400 C.

  - Process according to claim 4 characterized by the fact

  that the calcination temperature is between 600 and 800 C.

  6 - Process according to one of claims 4 and 5 characterized

  in that the calcination time varies between 30 minutes and 3 hours.

  7 - Process according to one of claims 1 to 6 characterized

  in that the controlled leaching is carried out using a nitric acid solution of concentration 1 to 14 N.

26- 008 1

  8 - Process according to claim 7 characterized in that the leaching is carried out using a nitric acid solution of concentration 3 to 9 N.

  9 - Process according to one of claims 1 to 8 characterized

  in that the amount of nitric acid used is equal to an amount ranging from the stoichiometric amount of the trivalent rare earths to an excess of up to 50% of

the stoichiometric quantity.

  - Method according to one of claims 7 to 9 characterized

  in that the leaching is carried out between 20 and 90 C.

  11 - Process according to claim 10, characterized in that the residence time in the lixiviation solution is included

between 30 minutes and 2 hours.

  12 - Process according to one of claims 1 to 11 characterized

  in that the leaching treatment is carried out at 60 ° C

  for a residence time of one hour.

  13 - Method according to one of claims 1 to 12 characterized

  in that an insoluble residue is separated from the leaching solution.

  14 - Method according to one of claims 1 to 13 characterized

  in that the leach solution contains more than 90% of trivalent rare earths including neodymium and less than 10%

  of cerium initially present in bastnaesite.

  - Process according to claim 14 characterized in that the concentration of rare earths expressed in oxides of land

  rare is between 150 and 500 g / l.

  16 - Method according to one of claims 1 to 15 characterized

  in that a pre-neutralization is carried out by addition of a base in the solution of rare earth nitrates until the pH is between 2 and 4, which makes it possible to eliminate the fluorine, the cerium and traces of thorium in a solid residue that

we separate.

  17 - Process according to claim 1 characterized by the fact

  that the extractant is a solvating extractant.

  18 - Process according to claim 17 characterized by the fact

  that the extracting agent is tributyl phosphate.